In the past decade, largely due to the proliferation of computers in the work place, the need to better understand the effects of lighting systems on workers' health and the need to design superior lighting systems have become paramount objectives. With the advent of video display terminals ("VDT") in the work place, as shown in FIG. 1, the relationship between workers, their tasks, and their environments has been altered significantly due to the fact that traditional "white paper tasks" have been substituted by VDT-based tasks. Lighting systems which were adequate before the VDT, are no longer satisfactory.
Lighting problems are now recognized among corporate executives as well as office workers, as the most prevalent health hazard in the work place. "Office Environment Index" survey of 1,041 office workers and 150 top executives, Steelcase Inc., Grand Rapids, 1989. The American Society of Interior Designers found that 68% of employees complain about the light in their offices. A Silicon Valley study concluded that 79% of VDT users want better lighting.
Typical fluorescent lights in the work place fall into three general categories, which are illustrated in FIGS. 2A, 2B and 2C. Illustrative of the first category is fixture 12, as shown in FIG. 2A, which is a "direct light", also referred to as a "down-light". Down lights project light in a straight-line path from the lamp to the work area. It is usually possible for a worker to actually see the down-light lamp from the work area. Down-lights are the most common type of light used in the work place.
As shown in FIG. 2B, fixture 14 is an example of the second category of fluorescent lights, known as "indirect lights", also referred to as "up-lights". In contrast to down-lights, up-lights project light onto a diffusing reflective surface which then directs the light into the work area. Ideally, up-light lamp output is controlled to provide a widespread light distribution in an upward direction to provide an even luminance over the whole ceiling which in turn provides the lighting for the space below.
Fixture 16 of FIG. 2C shows the third category of fluorescent light, which is a hybrid of the first two categories, referred to as a "direct-indirect light" or "up-down-light".
Within each light category various adaptations and accessories have been designed for the purposes of producing uniform, glare-free, shadow-free lighting. For example, as shown in FIG. 3, parabolic louvers 18 have been designed to serve as miniature baffles in a down-light for the purpose of minimizing the amount of light which directly enters the workers eyes as low angle glare. FIG. 4 shows an adaptation for an up-light, involving a lens 20 for refracting light upwardly in a uniform manner. However, until recently there was no definitive evidence of which general type of lighting is healthier for the worker.
In 1989 and 1990 Hedge et al., of Cornell University conducted a large scale experiment in the Xerox Corporation offices in Webster, N.Y., for the purpose of comparing state of the art down-lighting to state of the art up-lighting. The main goal of the study was to determine which system was preferable from the worker's perspective. The criteria were complaint frequencies and effect on work function. The type of down-light used in the study was a 3-lamp, 18-cell 2'.times.4' parabolic light. The up-light used was a partially-lensed system designed for open offices.
The results of the Cornell study show an overwhelming preference for the up-lights. Daily complaints of tired eyes and eye focusing problems were twice as frequent among workers who used down-lights relative to those who used up-lights. Almost half of those who used down-lights ended up modifying their lights, either by disconnecting lamps within the fixture, disconnecting the whole fixture or putting up some form of paper baffle to shield the fixture. In contrast, there was only a single reported instance of a worker modifying an up-light. Of all the workers in the study, approximately 80% expressed a preference for up-lights. Up-lights were also preferred with respect to work space glare, VDT screen glare and office light level. The two lighting systems were also compared in terms of worker productivity. 20% of the down-light users reported losing more than 15 minutes of work time per day due to eye focusing problems. In comparison, only 2% of the up-light users reported loss of more than 15 minutes of work time per day.
The Cornell study has brought a problem of tremendous magnitude into clear focus. Due to the fact that, prior to the Cornell study the advantages of up-lights were not well documented or established, and the fact that down-lights are initially somewhat less expensive to install compared to up-lights, most work places today have been equipped with down-lights. The field of "work places" which have made the regrettable decision to install down-lights spans across all industries, all around the world. Now, in view of recent studies, many individuals and institutions will desire to replace existing down-lights with up-lights.
The problem is that prior to the present invention, the only way to convert a down light into an up-light is to completely remove the down-light fixture and replace it with an up-light fixture. Such a conversion requires major structural changes to the ceiling, special permits to comply with local building codes, and substantial rewiring which must be performed by a skilled electrician. Moreover, such a conversion completely wastes the old down-light creating a significant disposal problem. All of this adds up to an extreme expense which will be prohibitive for most down-light users.
Prior modification devices have been disclosed which involve relocating the fluorescent lamp of a down-light for the purpose of decreasing the number of lamps and accordingly decreasing the amount of energy required to power the light. For example, U.S. Pat. No. 4,799,134 ('134) discloses a "delamping" device having an electrical connector for repositioning the lamp, a reflector above the lamp for redirecting the light downward and an additional V-shaped reflector below the lamp for scattering the light outward. However, this delamping device merely modifies a down-light to operate with less lamps, while retaining its overall down-light configuration. A similar delamping device is disclosed in U.S. Pat. No. 4,928,209 ('209) which includes a plug and substitute socket for relocating the fluorescent lamp to a central position below a reflector. Similar to the '134 device, the '209 device merely delamps a down-light, while retaining the overall down-light configuration. These references involve solutions to different problems from those solved with the present invention. In essence, the references fail to teach how to convert a down-light into an up-light.